As the topic states, is there any Address Book type app which would allow me to store numbers I infrequently use? An example would be ex-colleagues from a former employer (I rarely call these folks). The problem I have with storing them in the Contacts hub is that not only does it clutter my contact list but they also get synchronized to my Google account and I end up having a huge list of contacts there too.

Please feel free to tell me that this is a terrible idea and that I should just suck it up and live with a huge contact list. I'm just looking for the best way to organize my contacts.

Personally I would just store everything in the People hub. The navigation (jump lists and search) is really good that I don't care about having a long list. You can also organize contacts into Groups so that you can view updates from just those people.